Ink jet printing is a non-impact method that produces droplets of ink that are deposited on a substrate such as paper or transparent film in response to an electronic digital signal.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. Multiple orifices or nozzles also may be used to increase imaging speed and throughput. The ink is ejected out of orifices and perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the electrically charged ink droplets are passed through an applied electric field which is controlled and switched on and off in accordance with digital data signals. Charged ink droplets are passed through a controllable electric field, which adjusts the trajectory of each droplet in order to direct it to either a gutter for ink deletion and recirculation or a specific location on a recording medium to create images. The image creation is controlled by electronic signals.
In drop-on-demand systems, a droplet is ejected from an orifice directly to a recording medium by pressure created by, for example, a piezoelectric device, an acoustic device, or a thermal device controlled in accordance with digital data signals. An ink droplet is not generated and ejected through the nozzles of an imaging device unless it is to be placed on the recording medium.
To keep print heads properly printing, the print heads need to be maintained from time to time. The maintenance operations may include cleaning and wiping of the nozzle plate, pumping and purging ink nozzles to remove air bubbles, and firing the ink nozzles etc. One undesirable aspect of the print head maintenance is that the maintenance reduces the time available for printing and therefore lowers printing throughput.